Electric circuit breaker

ABSTRACT

An electric circuit breaker ( 1 ) comprises a switch ( 11 ) to be arranged in said electrical circuit ( 3 ); means ( 13 ) for causing said switch ( 11 ) to break said electrical circuit ( 3 ) in response to a tripping signal ( 14 ); means ( 17 ) for receiving (IF) and storing (MEM) a programmable current threshold command (CC); means ( 15 ) for detecting a current level (CL) in said electrical circuit ( 3 ); and processing means ( 16 ) for generating said tripping signal ( 14 ) depending on said stored programmable current threshold command (CC) and said detected current level (CL).

The present invention relates to an electric circuit breaker forprotecting an electrical circuit against excessive current loads.

Electric circuit breakers are typically used in electricity distributionnetworks at various locations in the network, in order to monitor thecurrent level flowing in the network, and to interrupt the electricalcurrent if the current level flowing through the electric circuitbreaker exceeds certain thresholds or limits.

In order to achieve an adequate protection in the low voltage portion ofthe network, thermo-magnetic circuit breakers are generally used. Athermo-magnetic circuit breaker inserted in an electrical circuit willautomatically break the electrical circuit to disconnect a portion ofthe network, if the current level through the electric circuit breakerexceeds a dangerous level, i.e. when an overload condition occurs. Inthis type of circuit breaker, this is typically accomplished by means ofa resistive thermal element which will modify its mechanical dimensionswith temperature due to the increased current level. A thermal elementwill, however, not instantaneously respond to an overload condition.Rather, the time required by the thermal element for varying itsmechanical dimensions depends on its thermal mass, and on the other handalso on the amount of overload current. The time required by the thermalelement for responding to the particular overload condition accordinglyvaries between fractions of a second and about one hour. Obviously, alsothe ambient temperature has an influence on this response time. Thenon-instantaneous response characteristics of the thermal element areappropriate for protecting the electrical circuit and thus the entirenetwork against a continuous overload condition caused e.g. by aparallel connection of too many loads to the electric circuit, whereasshort current spikes will not cause an unwanted tripping of the electriccircuit breaker. Such current spikes are generated when electric loadslike television sets or electric motors are switched on.

On the other hand, the non-instantaneous response characteristics makean electric circuit breaker with only a conventional thermal elementless suitable for protecting its associated network portion against veryhigh levels of overcurrent which may be caused e.g. by a short circuitcondition. In this situation a fast response of the circuit breaker isrequired.

In order to provide a fast response time in such extreme overloadconditions, a conventional electric circuit breaker for use in the LVnetwork therefore also comprises an electromagnetic element, e.g. acoil, which will generate a magnetic force depending on the amount ofcurrent flowing through the circuit breaker. If the force generated bythe magnetic element exceeds a certain force threshold, the magneticelement will trip the electric circuit breaker with some milli secondsof delay in order to prevent instantaneous damages in the network.

Besides this conventional type of thermo-magnetic circuit breaker, otherconventional types of electric circuit breakers comprise a thermalelement only, or an electromagnetic element only, for breaking theelectrical circuit when an overload condition has occurred.

Each of these and other types of conventional electric circuit breakershas a so-called rated current. This parameter describes the currentlevel beyond which the circuit breaker is supposed to break theelectrical circuit. A current level above the rated current levelconstitutes an overload condition which will eventually lead to thetripping of the electric circuit breaker. The rated current isdetermined by the design of the circuit breaker, e.g. the size, thermalmass, mechanical bias and the like of the thermal and/or electromagneticelements. Nowadays, a variety of electric circuit breakers is on themarket for a variety of different rated currents, adapted to the varietyof needs which arise from the existing variety of types of consumers,load levels and network load constraints. However, one or more of theseparameters of an electrical installation may change sometimes forvarious reasons. In a power distribution network a need may arise toupdate the tripping current level or the degree of protection for thecircuit protected by the circuit breaker. To achieve this withconventional circuit breakers, it is necessary to replace the existingelectric circuit breaker having a first rated current by anotherelectric circuit breaker having another rated current adapted to the newsituation. This is laborious, time consuming and can be particularlydisadvantageous in large electricity distribution networks. A change ofthe tripping current level during the ongoing operation of the circuitbreaker is impossible. The necessity to provide and install a variety ofdifferent circuit breakers with a variety of given rated currents leadsto inflexibilities with adverse impacts on the costs for networkmaintenance and administration. More flexibility in this regard would behighly desirable.

The present invention has been made in order to solve these and otherproblems associated with the prior art. An electric circuit breakeraccording to an embodiment of the present invention comprises a switchto be arranged in the electrical circuit which is to be protectedagainst excessive current loads. The circuit breaker furthermorecomprises first means for causing said switch to break the electricalcircuit in response to a tripping signal. Means are provided forreceiving and storing a programmable current threshold command. Thecircuit breaker detects a current level in the electrical circuit, andprocessing means are provided for generating said tripping signaldepending on said stored current threshold command and said detectedcurrent level.

This embodiment of an electric circuit breaker according to the presentinvention is advantageous in that the load protection characteristics ofthe circuit breaker are provided programmable. In this way an electriccircuit breaker is obtained which is suitable for a variety ofconsumers, load levels and network load constraints, without the need toperform replacement work or to keep a large number of different types ofcircuit breakers available.

The programming of the electric circuit breaker can be performed in avariety of different ways. Preferably, the electric circuit breakerincludes power line communication means for receiving current thresholdcommands via the electric circuit protected by the circuit breaker. Suchreceived current threshold commands are stored by the electric circuitbreaker until another current threshold command is received. Suchcommands can be generated by a central facility for administrating agiven network section which comprises a plurality of consumers andassociated electric circuit breakers. It is advantageous to adapt thecentral facility such that individual current threshold commands can beaddressed to individual circuit breakers in the network section. Thiswill allow the network operator to remotely administrate an individualconsumer connected to a particular electric circuit breaker with a highdegree of flexibility and low administration costs. For example, changesin the supply contract relating to the maximum admissible currentconsumption can be implemented quickly by reprogramming the electriccircuit breaker by remote administration.

In addition or alternatively, it is furthermore advantageous to providethe central facilities such that a current threshold command can beaddressed to a group or to all of the electric circuit breakers in thenetwork section. By way of example, in response to the occurrence of aglobal overload condition in the entire network section administrated bythe central facility, appropriate, e.g. lower current thresholds can beprogrammed into a large number of electric circuit breakers, in order toprevent a global breakdown or blackout without the need to switch offthe entire network section. Such global overload conditions may e.g.occur if a large number of consumers simultaneously draws current fromthe network section at a level which is close to but below the normalcurrent threshold applicable to the consumers. Similarly, under lightload conditions in the network section it would be advantageous toprogram higher current threshold into a group or all of the electriccircuit breakers of that section in order to allow a higher individualconsumption of current for the consumers of that section.

Alternatively or in addition to the provision of means for receivingprogrammable current threshold commands via power line communicationover the electrical circuit to which the electric circuit breaker isconnected, it can be advantageous to provide the electric circuitbreaker with a user interface to receive programmable current thresholdcommands from an operator e.g. through a keyboard, or from a programmerdevice, e.g. a suitably programmed personal computer, through a suitablestandard interface like RS232, USB, blue tooth or the like. Interfaceswith a high level of electrical insulation, like flag port devices or inaccordance with IEC 61107/EN 61107/IEC62056-21 are particularlyadvantageous.

Preferably, said means for receiving a programmable current thresholdcommand is adapted to store a plurality of current thresholds andassociated response times as specified by the received current thresholdcommand. Preferably, said processing means is adapted to generate saidtripping signal when the detected current level in the electricalcircuit protected by the electrical circuit breaker has continuouslyexceeded a stored programmed current threshold for a duration determinedby the associated programmed response time. In this way it can beachieved that the response time of the electric circuit breaker isprogrammable and dependent on the level of overcurrent flowing in theelectrical circuit. Preferably, the response times are programmed todecrease with the associated current thresholds increasing, such thanthe response time for more severe overload conditions will be shorterthat the response time for less severe overload conditions. As analternative to specifying programmable current thresholds and/orassociated response times in the current threshold command, it can beadvantageous to provide means for storing a plurality of predefinedfunctional relations defining the associated response times for avariety of current levels, and to provide the processing means to selectone of these predefined relations in accordance with the received andstored programmable current threshold command.

As a further alternative, said current threshold command can also beused to specify only the response time until said processing meansresponds to one or more predefined stored current thresholds with thegeneration of said tripping signal which causes said switch to break theelectric circuit.

Advantageously, the electric circuit breaker furthermore comprises meansfor receiving a switch command, that is a circuit open command orcircuit close command, and means for operating said switch to open andclose the electrical circuit in accordance with the received switchcommand. Such switch command can be transmitted via power linecommunication and allows a remote control of the electric circuitbreaker of individual consumers or of groups of consumers from centraladministration and control facilities.

Advantageously, the electric circuit breaker furthermore comprisessecond means for causing the switch to break the electrical circuit if acurrent flowing in the electrical circuit exceeds a predetermined ratedcurrent. According to this embodiment, the switch will be caused tobreak the electrical circuit if the current flowing through the electriccircuit breaker exceeds a predetermined rated current for more than agiven duration. Under normal conditions of the electric circuit breaker,the switch will trip in response to the tripping signal generated by theprocessing means in accordance with a variable current threshold whichcan be programmed from the external into the electric circuit breaker.The second means advantageously provides upper response limitsassociated with current levels above the rated current for the electriccircuit breaker to break the electric circuit, in order to take accountof the possibility that a fault occurs in the electric circuit breakerand tripping under a load condition above the programmed threshold doesnot work. Preferably, the second means for causing the switch to breakthe electrical circuit as well as the switch form an integral unit. Itis particularly convenient to also incorporate said first means intothis integral unit.

Advantageously, an electric circuit breaker according to the presentinvention is incorporated in a power meter or energy meter for measuringthe electric energy consumption of a consumer. Advantageously, theelectric circuit breaker comprises means like a lever or button forenabling an operator to manually break or close the electric circuit.

Further advantageous embodiments of the present invention are defined inthe dependent claims.

In the following, specific embodiments of the present invention will bedescribed with reference to the accompanying drawings. In the drawings,similar or corresponding elements have been denoted with the samereference signs.

FIG. 1 shows an overview of an electric power distribution networkcomprising a plurality of electric circuit breakers;

FIG. 2 shows a block diagram of a first embodiment of an electriccircuit breaker according to the present invention;

FIG. 3 a, b show t-I diagrams to illustrate the operation of embodimentsof the electric circuit breaker according to the present invention;

FIG. 4 shows an embodiment of an electric power distribution networkcomprising central control facilities;

FIG. 5 shows a second embodiment of an electric circuit breakeraccording to the present invention;

FIG. 6 shows a third embodiment of an electric circuit breaker accordingto the present invention;

FIG. 7 shows an advantageous embodiment of the element 13 for causingthe switch to break the electrical circuit in response to a trippingsignal;

FIG. 8 shows a flow diagram to illustrate the operation of an embodimentof the processing means of the electric circuit breaker;

FIG. 9 shows an extension of the flow diagram shown in FIG. 7;

FIG. 10 shows a first embodiment of a hardware implementation of theprocessing means; and

FIG. 11 shows a second embodiment of a hardware implementation of theprocessing means.

FIG. 1 shows a typical electricity distribution network for distributingelectrical energy generated by a power plant (not shown) to a pluralityof consumers (H1, H2, . . . Hn). The electricity is distributed over alarge geographical area by means of a so-called high voltage network HV,which connects the one or more power plants feeding this high voltagenetwork HV with a plurality of so-called primary substations Tp. Theprimary substations Tp transform the high voltage (e.g. 380 kV inEurope) carried over the HV network into a medium voltage of e.g. 20 kVfor regional distribution of the energy. The medium voltage distributionnetwork MV connects the one or more primary substations Tp with one ormore secondary substations Ts which transform the medium voltage carriedover the MV network into a low voltage carried over a low voltagenetwork LV for distribution to a large number of consumers H1, H2, . . ., Hn. In Europe, the typical low voltage level is 220 to 240 volt,depending on national regulations. The three power distribution subnetworks, that is the HV network, MV network and LV network, requireelectric circuit breakers at various locations in order to enable thenetwork to appropriately react to fault conditions like short circuitsor temporary overload conditions which would otherwise lead to adestruction of the network. Reference numeral 1 denotes an electriccircuit breaker located at the consumer premises of consumer Hn.

Reference numeral 2 denotes a supply line connecting the consumer Hnwith the LV network. F denotes a fuse provided in the line 2 for safetyreasons in order to prevent that an excessive current I causes damage tothe LV network. Reference numeral 3 denotes a power supply line at theconsumer premises Hn, e.g. a power supply line installed inside abuilding. Power supply line 3 is connected with the power supply line 2through the electric circuit breaker 1. The power supply line 3 in turnfeeds a plurality of electric loads L1, L2, . . . , Lk through switchesas appropriate. L denotes a lever arranged at the electric circuitbreaker 1 to be externally accessible by an operator, for manuallyconnecting or disconnecting the power supply 3 and the power supply line2. Structure similar to that what has been shown in greater detail forthe consumer Hn may be found in the other consumers H1, H2, . . . .

FIG. 2 shows a first embodiment of an electric circuit breaker accordingto the present invention. In the block diagram of FIG. 2, referencenumeral 1 denotes the electric circuit breaker which is connectedbetween the power supply line 2 and the power supply line 3 shown inFIG. 1. The character n across the power supply lines 2 and 3 and otherlines in the electric circuit breaker indicates that while for reasonsof simplicity a single phase arrangement is shown in the figure, a polyphase design is not different in principle from the single phase designshown in this and other drawings of the present invention, and that thepresent description applies to single phase power supply systems (n=1)as well as to poly phase power supply systems, e.g. n=3 Referencenumeral 11 in FIG. 2 denotes a switch connected in series with firstmeans 12 for thermo-magnetically detecting the level of the current Iflowing through the power supply line 3. Such thermo-magnetic currentdetector means 12 are as such well known in the art, and a detaileddescription of the thermo-electric current detector 12 is, therefore,not necessary. As indicated by the dotted line in FIG. 2, thethermo-magnetic current detector means 12 is mechanically coupled withthe switch 11 in order to cause the switch 11 to break the electricalcircuit established by the power supply line 3 and its connectedelectrically loads, in short the electrical circuit 3, if the current Iflowing in the electrical circuit 3 exceeds a predetermined ratedcurrent. This predetermined rated current is determined by the design ofthe thermo-magnetic current detector 12. This element 12 typicallycomprises e.g. a resistive element not shown in FIG. 2, which willchange its temperature in accordance with the current load I. A bi-metalarrangement can conventionally be used to transform the change oftemperature into a mechanical displacement which is then taken to tripthe switch 11 and break the electrical circuit 3. The current detector12 furthermore comprises electromagnetic current detection meansmechanically coupled with the switch 11, as indicated by the dotted linein FIG. 2. These electromagnetic current detection means can beimplemented e.g. by means of a coil connected in series with the switch11, such that an electromagnetic force is generated by that coil inaccordance with the level; of current I flowing in the electric circuit3. If this magnetic force generated by the current detector 12 exceeds apredefined force threshold determined by the design of the currentdetector 12 and/or the switch 11, this will cause the switch 11 to breakthe electric circuit 3. L denotes an externally accessible lever L toenable a user to manually trip the switch 11. A variety of designs ofthe switch 11, the thermo-magnetic current detector 12 as well as theelectrical and mechanical coupling between the elements 11 and. 12 is assuch well known in the art and suitable for the present invention.

Reference numeral 15 denotes a second means for detecting the level ofcurrent I flowing in the electrical circuit 3. In FIG. 2, the means 15for detecting the current level I is shown to be connected in serieswith the switch 11 and the thermo-magnetic current detection means 12. Rdenotes a resistive element in series with the electric circuit 3.Reference numeral 151 denotes an amplifier means for detecting thevoltage drop occurring across the resistive element R in proportion withthe current level I, and outputting a corresponding current leveldetection signal CL. At this stage it is important to note that thereexists a variety of well known current detection circuits andtechniques, and the specific implementation depicted in FIG. 2 shall notbe construed to limit the current detection means 15 to theimplementation shown. As an alternative to the shunt resistor R it wouldalso be possible to adopt a current transformer, e.g. realized by meansof an additional winding magnetically coupled; with a coil in thecurrent detector 12 which generates the magnetic force for tripping theswitch 11 in case of excessive current levels I. This additional windingtogether with said coil will constitute a transformer in order toimplement the current detector 15. Other possibilities of implementingthe current detector 15 comprise hall effect devices, magneto resistorsand Rogosky coils, all of them being well known as such to be suitablefor the design of current detection means.

Reference numeral 13 denotes a means for causing the switch 11 to breakthe electrical circuit 3 in response to a tripping signal 14. The means13 preferably comprises an electromagnetic coil for magnetizing amovable member made from soft iron in accordance with the trippingsignal 14. Upon magnetization, a magnetic force will be exerted upon thesoft iron member in the element 13. This member is mechanically coupledwith the switch 11, as indicated by the dotted line in FIG. 2, such thatin response to the tripping signal 14, the element 13 will cause theswitch 11 to break the electrical circuit 3. The element 13 can beimplemented in a variety of ways in order to achieve the desiredfunction, to trip the switch 11 in response to a tripping signal 14. Analternative implementation of the element 13 exploits the well knowneffect of magnetostriction and comprises a member made frommagnetostrictive material which is subjected to a magnetic fieldgenerated by a coil in the element 13 which receives the tripping signal14, such that upon this tripping signal 14, the magnetostrictive elementwill change its mechanical dimensions. This element is mechanicallycoupled to the switch 11, such that the switch 11 will trip upon theapplication of the tripping signal 14 to the element 13.

Reference numeral 17 denotes a means for receiving a programmablecurrent threshold command CC. This current threshold command is anexternal command, that is a command not generated autonomously by theelectric circuit breaker 1. This current threshold command CC isreceived by a suitable communication interface IF in the means 17 andthen passed on to a memory MEM wherein the received current thresholdcommand can be stored. The communication interface IF can be a powerline communication interface for receiving current threshold commands CCthrough the power supply line 2 and the LV network connected to thepower supply line 2. The communication interface IF can also be designedto receive current threshold commands CC through a standardcommunication interface like RF 232 or USB or some kind of proprietarywire based or infrared or blue tooth interface for communication with ahand held programming device or a personal computer (PC). Alternativelyor in addition, the communication interface IF can comprise a key padfor receiving current threshold commands CC through manual user input,preferably in encrypted form or subject to successful userauthentication in order to avoid an unauthorized or illegal access tothe means 17 for receiving programmable current threshold commands.

Reference numeral 16 denotes processing means which receive informationCL regarding the detected current level from the current detection means15, and which processing means furthermore receive information about thecurrent threshold command stored in the memory MEM of the currentthreshold command receiving and storing means 17. The processing means16 outputs the tripping signal 14 as a result of processing operationswhich depend upon the input of the current level information CL and thecurrent threshold command stored in the memory MEM, and preferably alsodepending upon temporal characteristics of the detected current levelCL, as will be explained in greater detail further below. The processingmeans 16 may be implemented in hardware or by means of suitablyprogramming a micro controller. The processing means 16 also comprisesdriver circuitry to drive the element 13, specific embodiments of whichwill be shown below. If a micro controller is adopted for implementingthe processing means 16, the micro controller can also take over atleast some of the functions of the current threshold command receivingand storing means 17. Embedded micro controller solutions are availableon the market, comprising on chip interfaces which can be used toimplement the command receiving interface IF of the element 17.

In order to explain the operations performed by the processing means 16in greater detail by way of example, reference will be made in thefollowing to the diagram shown in FIG. 3 a.

FIG. 3 a shows a t-I diagram to illustrate the reaction of the electriccircuit breaker to various load conditions, that is levels of currentflowing through the circuit breaker. The horizontal axis of this diagramindicates the level of current I, while the vertical axis of thisdiagram indicates the response time t of the circuit breaker for a givencurrent level I.

In FIG. 3 a, reference numeral 31 denotes a first section of a curverepresenting a functional relation between current levels in a currentinterval between I_(R) and I₂ and the associated response time.Reference numeral 32 denotes a second section of the curve for currentlevels above I₂. The curve 31, 32 describes the behaviour of thethermo-magnetic current detector 12, I_(R) denoting the rated current ofthe current detector 12. Curve sections 331 to 333 for current intervalsbetween I₃, I₄, I₅, respectively on the one hand and I₁, on the otherhand, as well as the curve section 334 for currents between I₁ and I₂,describe the behaviour of the current detector 15, processing means 16and triggering means 13. In the following, the operation of the circuitbreaker shown in FIG. 2 will be explained with reference to these curvesshown in FIG. 3 a.

In this embodiment, the electric circuit breaker stores in the memoryMEM in the command receiving and storing means 17 a current thresholdcommand CC which identifies one of the curves 331, 332 and 333associated with respective current thresholds I₃, I₄, I₅, respectively.This current threshold command was previously received from the externalthrough the command interface IF of the electric circuit breaker. Inorder to explain the operation of the electric circuit breaker, at firstan operating condition is assumed, that the load current I through theelectric circuit breaker is below the programmed current threshold, sayI₄ in FIG. 3 a, presently stored in the memory MEM. In this case, theprocessing means 16 will apply a characteristic curve 332 defined by thestored current threshold command I4. Since the current load is below thecurrent threshold I₄, the processing means 16 will not generate atripping signal, and the switch 11 will remain closed such that thecurrent I will continue to flow. Assuming now the occurrence of anoverload condition resulting in a current I larger than the programmedcurrent threshold I₄, the processing means will process the detectedcurrent level reported from current detector 15 in S accordance with theprogrammed current threshold I₄ by means of measuring the time for whichthis overload condition continuously prevails. If the duration of theoverload condition reaches the response time associated with thedetected current level I, as represented by curve 332, the processingmeans will generate the tripping signal 14 which will cause the switch11 to break the electric circuit and hence, terminate the flow ofcurrent in the electric circuit 3. In the example shown in FIG. 3 a, anoverload condition in the interval between 14 and I₁ will result in aresponse time between about 200 seconds for current level just above theprogrammed threshold I₄, and about 100 seconds if the current levelapproaches I₁. In other words, the processing means 16 is adapted togenerate the tripping signal in response to a detected overloadcondition in such a way, that the response time also depends on theamount of overload. In the exemplary diagram of FIG. 3 a, all the threecurves 331, 332 and 333 join a curve 334 at the current level I₁. If anoverload condition above the threshold I₁ is detected by the currentdetector 15 in FIG. 1, the processing means 16 will generate thetripping signal 14 as soon as the overload condition above the thresholdI₁ has prevailed for more than about 1 sec., as represented by the curvesection 334. The response times t associated with the various currentlevels may be predefined, or they may be provided programmable by meansof the current threshold command CC.

The curve section 31 represents the function of the thermal element inthe thermo-magnetic current detector 12 shown in FIG. 2. From FIG. 3 ait is evident, that due to the operation of the processing means 16 inconjunction with the current detector 15 and the tripping means 13 asjust described, the thermo-magnetic current detector 12 should not getthe opportunity to cause the switch 11 to break the electric circuit,because for a given overload condition, the processing means 16 willgenerate the tripping signal 14 with a shorter response time than thethermal response time depicted by the curve section 31 of thethermo-magnetic current detector 12. In the embodiment shown in FIG. 3a, only for extremely high overload conditions approaching the magneticforce threshold I₂ of the thermo-magnetic current detector 12, theresponse time of the thermo-magnetic current detector 12 and inparticular the response time of the electromagnetic components of thatcurrent detector 12, will be shorter than the response time of theprocessing means 16. Accordingly, the thermo-magnetic current detector12 offers a backup function to make sure that the electric circuitbreaker will respond to overload conditions with an interruption of theelectric circuit 3 even if a fault occurs in any of the elements 13 to17 shown in FIG. 2.

In the specific example shown in FIG. 3 a, the current threshold I₁ maybe predetermined in order to provide a fixed upper current limit. It maycoincide with the rated current I_(R) of the thermo-magnetic currentdetector 12, because in this example, any load condition above thecurrent level I_(R) will by virtue of the thermo-magnetic currentdetector 12 cause the switch 11 to break the electrical circuit 3,unless the processing means 16 causes an earlier tripping of the switch11. It is important to note that this specific example shall not beconstrued to limit the invention in any way. Of course, it is possibleto adapt the current thresholds I₁ to I₅ shown in FIG. 3 to a variety ofdifferent needs in accordance with the particular design withoutdeparting from the principles of the present invention. It is, however,preferable to program the electric circuit breaker such that theprogrammed t-I curve remains below the curve sections 31, 32 of thethermo-magnetic current detector 12.

While the embodiment of FIG. 3 a provides a single programmable currentthreshold only, it can be advantageous to adapt the processing means 16such that the current threshold command CC identifies individual t-Icurves to be applied by the processing means 16 in processing theinformation about the detected current level CL. The plurality of curvesavailable for selection can be defined in the processing means 16 or inthe current threshold command receiving and storing means 17 in the formof tables or in the form of mathematical equations characterizing theset of curves in parameterised form.

FIG. 3 b shows another example of a t-I curve adopted by the processingmeans 16. In this embodiment, not only the current thresholds I₁, I₃,I₄, I₅ are provided programmable, but also the response times t1, t3,t4, t5 associated with the current intervals between adjacentthresholds, as depicted in FIG. 3 b. In this embodiment, a currentthreshold command CC contains at least one current threshold I_(j) andat least one associated response time tj. While all current thresholdsI₁, I₃, I₄, I₅ are shown to be less than I_(R), this is not mandatory.Current thresholds above I_(R) can be programmed with associatedresponse times below the curve 31, 32 in FIG. 3 b.

FIG. 4 shows an embodiment of an electric power distribution networkcomprising central control facilities for generating current thresholdcommands CC. In FIG. 4, elements similar to the elements shown in FIG. 1have been denoted with the same reference signs. With respect to theseelements, reference is made to the description for FIG. 1 in order toavoid repetitions.

In FIG. 4, S denotes a secondary substation for transforming the voltagecarried on the medium voltage network MV into the low voltage carried onthe low voltage network LV. To this end, the secondary substation Scomprises a transformer Ts as described above. CBT denotes communicationmeans associated with the secondary substation S. The communicationmeans CBT can generate current threshold commands addressed toindividual ones or to specified groups of electric circuit breakers 1 atthe consumer premises H1, H2, . . . , Hn which are connected to the LVnetwork section supplied by the secondary substation S. Referencenumeral 24 denotes a coupling means, e.g. a coupling capacitor, forcoupling the current threshold commands CC generated by thecommunication means CBT to the power supply line 2 of the LV network.Accordingly, in the embodiment shown in FIG. 4, the LV network sectionsupplied by the secondary substation S not only serves to distributeelectrical power to the consumers H1, H2, . . . , Hn, but also serves asa communication medium for transmitting the current threshold commandsCC to individual electric circuit breakers 1. In this embodiment, thecommunication means CBT comprise means for detecting the present loadcondition of the network section. The communication means CBT comprisessuitable processing facilities to process the detected load condition,that is the power presently supplied by the secondary substation S toits LV network section, in order to generate appropriate currentthreshold commands to selected ones or to all electric circuit breakers1 at the consumer premises H1, H2, . . . , Hn of that LV networksection. If the overall load condition approaches a current limit orpower limit e.g. of the secondary substation S, the communication meansCBT is programmed to generate current threshold commands and broadcastthem via the LV network section to the consumers H1, H2, . . . , Hn ofthe network section. The electric circuit breakers 1 at the consumerpremises receive the broadcast current threshold command and store it intheir memory MEM. In this way, as a reaction to a critical loadsituation in the entire LV network section of the secondary substationS, all electric circuit breakers 1 can lower their current thresholdssuch that only the consumers presently drawing a large amount of currentwill be disconnected from the LV network section. In this way, acomplete shut off of the entire LV network section can be avoided. If aneffected consumer disconnects some of the loads L1, L2, . . . , LK fromthe power supply line 3, he will be able to reconnect to the LV networkupon operation of the leaver L of the electric circuit breaker 1.Accordingly, in the embodiment of FIG. 4 the communication means CBT canadaptively control the maximum power which each consumer may draw fromthe network in accordance with the present overall load condition, toprevent the occurrence of severe overload conditions which would requirethe shut down of the entire LV network section. Under light loadconditions the CBT will generate appropriate broadcast current thresholdcommands in order to increase the current thresholds programmed into theelectric circuit breakers 1 at the various consumer premises H1, H2, . .. , Hn.

It can be particularly advantageous to distinguish between differenttypes of consumers. There are some types of consumers, e.g. hospitals,which need to be supplied with electric power in any case. For othertypes of consumers, e.g. for normal households, it may be assumed that atemporary reduction of the current threshold will have less severeimpacts. Accordingly, it may be advantageous to provide a consumer typeindication together with a programmable current threshold command CCfrom the communication means CBT, and to store a correspondingpredefined type indication in each of the electric circuit breakers inaccordance with the type of consumer. This consumer type indicationallows that in order to prevent a complete black out under severe loadconditions, the CBT will at first lower the current thresholds of suchtypes of consumers which are less dependent on a guarantied subscribedpower level, and to gradually extend the reduction of the currentthresholds to other types of consumers, if this forms out to benecessary to prevent a complete black out.

It is important to note that while this concept has been shown anddescribed with regard to consumers connected to an LV network sectionsupplied by a secondary substation S, the same concept can also beapplied in other network portions higher up in the network hierarchy.E.g., electric circuit breakers programmable as described above, can beprovided to protect sections of the MV network, with communication meansbeing located at the primary substations Tp which monitor the presentload conditions and which generate appropriate current thresholdcommands to the electric circuit breakers in the MV network and/or tothe electric circuit breakers at the consumer premises supplied by theaffected MV network section.

Reference numeral 23 in FIG. 4 denotes means for connecting thecommunication means CBT with central administration and controlfacilities 21 through a public wireless telecommunication network 20.The central administration and control facilities 21 can be provided toadministrate larger portions of the network in a hierarchical fashion,using the communication means CBT associated with the secondarysubstations S as an intermediate communication node. The facilities 21can be used to administrate supply contracts, e.g. regarding the maximumpower subscribed by an individual consumer Hi, and to programcorresponding current thresholds and/or response times into the electriccircuit breaker 1 of consumer H_(i) in accordance with the contractualprovisions agreed with the individual consumer H_(i), without the needto have service staff visit the consumer premises.

FIG. 5 shows an embodiment of an electric circuit breaker 1 in theelectric power distribution network shown in FIG. 4. In the electriccircuit breaker 1 of FIG. 5, elements similar to the elements shown inFIG. 2 have been denoted with the same reference numerals, such thatwith regard to these elements reference can be made to the descriptiongiven for FIG. 1.

In the embodiment of FIG. 5, the current threshold command receiving andstoring means 17 is adapted to receive the current threshold commands CCvia power line communication from the power supply line 2 which connectsthe consumer Hn to the LV network. Reference numeral 171 denotes acapacitive coupling means for taking the power line communicationsignals generated by the communication means CBT in FIG. 4 from thepower supply line 2. These power line communication signals carrying thecurrent threshold commands CC are received by the command interface IFand stored in the current threshold command memory MEM, as describedabove. A large variety of ready made products and solutions is availableon the market for imlementing power line communication systems. Any ofthese power line communication solutions can be adopted for transmittingcurrent threshold commands CC to the electric circuit breaker 1, suchthat a detailed description of power line communication technology maybe omitted here.

FIG. 6 shows a third embodiment of an electric circuit breaker 1according to the present invention. This embodiment differs from theembodiment of FIG. 5 in the provision of energy metering means 18 formeasuring and counting the energy drawn by the consumer from the powerdistribution network through the power supply line 2. In the embodimentshown in FIG. 6, the energy metering means 18 receive a current leveldetection signal CL from the current detector 15. The energy meteringmeans 18 calculates the energy from the detected current level CL andthe detected supply voltage U and accumulates at least the active energydrawn from the power supply network. The accumulated amount of energy isdisplayed on a display 19. All other components of the electric circuitbreaker 1 of the embodiment of FIG. 6 correspond to the components shownin the second embodiment of FIG. 5. In this respect, reference is madeto the description already given above.

FIG. 7 shows an advantageous embodiment of the means 13 for causing theswitch to break the electrical circuit in response to a tripping signal.This embodiment is suitable for any of the circuit breaker embodimentsherein described. In FIG. 7, elements similar to or identical withelements shown in the preceding figures have been denoted with the samereference numerals. With regard to these elements reference is made tothe description given above. In the embodiment of FIG. 7, the means 13comprises an electromagnetic coil 131 which is connected to receive thetripping signal 14 from the processing means 16. The coil 131 magnetizesa movable element 132 which is mechanically coupled to the contacts 111of the switch 11. Moreover, the movable element 132 is also coupled withthe lever L for manually operating the switch 11. Reference numeral 133denotes an auxiliary switch mechanically coupled with the movableelement 132. The auxiliary switch 133 is connected in series with thecoil 131, such that the energization of the coil 131 by the trippingsignal 14 depends on the state of the auxiliary switch 133. Referencenumeral θ11 denotes a displacement of the movable element 132, e.g. anangle, which is required to open the contacts of the switch 11.Similarly, θ133 denotes a displacement of the movable element 132, e.g.an angle, which is required to open the auxiliary switch 133. Accordingto the embodiment shown in FIG. 7, the switch 11 and the auxiliaryswitch 133 are constructed such that the displacement θ133 required toopen the auxiliary switch 133 is larger than the displacement θ11required to open the switch 11. When the processing means 16 generates atripping signal 14, this will energize the coil 131 until thedisplacement of the movable element 132 is large enough to open theauxiliary switch 133. This displacement will then surely be large enoughto reliably open the contacts 111 of the switch 11. At the same time itis achieved that a current through the coil 131 will be neither highernor lower than necessary and will not flow longer than necessary forreliably opening the switch 11. The duration for which the processingmeans 16 generates the tripping signal 14, is uncritical.

According to an advantageous modification of this embodiment, themechanical coupling of the lever L with the switch 11 is made dependenton whether the coil 131 is energized or not. If the coil 131 isenergized, then the lever 11 is decoupled from the switch 11. To thisend an electromagnetic coupling element (not shown) can be provided forselectively coupling or decoupling the lever L from the switch contacts111. The electromagnetic coupling element can have a movable hook, cam,tappet or any other engagement means which can be biased e.g. by meansof a spring, to mechanically couple the lever L with the contacts 111 ofswitch 11. The electro magnetic coupling element has means to electromagnetically withdraw the engagement means to decouple the lever L fromthe switch contacts 111 when the coil 131 is energized. When theprocessing means 16 outputs a continuous tripping signal, for instancein response to an external circuit interrupt command (which has causedthe switch 11 to break the electrical circuit 3) and a user then triesto move the lever L into the closed position of the switch 11 tore-establish the electrical circuit 3, this will result in that theauxiliary switch 133 will close before the switch 11 can close, due tothe fact that because the displacement required to open the auxiliaryswitch 133 is larger than the displacement required to open the switch11, the switch 133 will close earlier than switch 11 can close. Thiswill then energize the coil 131 and decouple the lever L from the switchcontacts 111 before the switch contacts 111 can close the electricalcircuit. The energized coil will furthermore generate a force upon thelever L which is perceivable by the user, to urge the lever back intothe open position. On the other hand, if there is no longer a trippingsignal from the processing means 16, the lever can be moved back intothe closed position.

The electromagnetic coupling element (not shown) can either comprise itsown actuator (e.g. a coil) electrically connected in series with thecoil 131, or the electromagnetic coupling element can be connected intothe magnetic circuit which is energized by the coil 131, such thatwhenever the coil 131 magnetizes the movable element 132, a magneticforce is exerted also upon the engagement means to withdraw fromengagement with the switch contacts 111.

FIG. 8 shows a flow diagram to illustrate the operation of an embodimentof the processing means. In this embodiment, the processing meanscomprises a micro processor and associated program and data memory, aswell as input/output port facilities. Such hardware structures areavailable on the market e.g. in the form of embedded micro controllersolutions wherein the micro processor as well as the required peripheraldevices like memories and I/O ports are integrated on a single chip. Theembodiment shown in FIG. 8 is but one of a large variety of possibleimplementations of the processing means 16 in any of the previouslydescribed embodiments of the electric circuit breaker 1, as will bereadily apparent to those skilled in the art. In this embodiment, themicro processor in the processing means 16 is programmed to perform theflow of operations shown in FIG. 8. This flow of operations achieves theprocessing of the detected current level CL and the generation of thetripping signal 14 depending on a stored programmed current thresholdcommand maintained in the memory MEM, which indicates a programmedcurrent threshold Ij and the associated response time Tj. The flow ofFIG. 8 implements a retriggerable measurement of the duration of anoverload condition when the detected current level CL is above thecurrent threshold Ij, wherein a non-steady overload condition will notlead to the generation of a tripping command 14, as will be explained inthe following.

S1 in FIG. 8 denotes an operation to initialise an incremental index ito take the value 1. This incremental index will be used to identify oneof K sub-intervals Ti of the programmed response time Tj. The flow ofoperation in FIG. 8 queries for each of the K sub-intervals Ti whetherthe overload condition prevails. If and only if the overload conditionwas present for K successive sub-intervals Ti, the tripping signal 14will be generated to break the electrical circuit 3.

In the operation S2 of FIG. 8, a timer is loaded with the value Ti. Theoperation S3 serves to check whether the timer set in the operation S2has expired (branch Y) or not (branch N). After the expiry of thesub-interval Ti, the flow proceeds to the operation S4 wherein it ischecked whether the current level CL is larger than the programmedcurrent threshold Ij. In the negative case (branch N), the flow returnsto the operation S1 to reinitialise the incremental index i. In theaffirmative (branch Y of operation S4), the flow moves on to theoperation S5 in order to increment the index i. Then, in operation S6 itis checked whether the incremental index exceeds a value K whichsatisfies the condition that K times Ti equals the programmed responsetime Tj. In the negative, the overload condition did not yet prevail formore than the programmed response time Tj and the flow returns to theoperation S2. In the affirmative (branch Y), the flow proceeds to theoperation S7 to generate a tripping command, that is the tripping signal14 of the processing means 16.

The flow of operations shown in FIG. 8 can be initiated as an interruptroutine which will be executed whenever the current detector 15indicates that a programmed current threshold Ij has been exceeded. Inthe alternative, the flow of FIG. 8 can be executed repeatedly atregular time intervals, e.g. triggered by a timer interrupt, or the flowof operations S1 to S7 can be implemented as a subroutine repeatedlycalled by other software routines implemented for execution on the microcontroller, e.g. in a polling mode. If the current threshold commandindicates a plurality of programmed current thresholds Ij and associatedresponse times Tj, as shown e.g. in FIG. 3 b, the flow of operations inFIG. 8 will be executed for each programmable pair of current thresholdsIj and associated response times Tj.

FIG. 9 shows an advantageous extension which provides a safety checkwhen a tripping signal has been generated, in order to confirm that thedetected current level CL has a matter of fact reached zero. In theoperation S8 it is checked whether an active tripping signal is present.As soon as a tripping signal exists (branch Y in the operation S8), acheck is made whether the current level CL has reached zero. In thenegative case (branch N in the operation S9), the flow proceeds to theoperation S10 to set an alarm condition because of the detection of acurrent level larger than zero despite the generation of a trippingcommand for the switch 11. This alarm condition can be an audio and/orvisual indication at the electric circuit breaker 1. More preferably,the electric circuit breaker 1 comprises means to report this alarmcondition to the communication means CBT and/or to the centraladministration and control facilities 21 which will then takeappropriate action.

FIG. 10 shows a further embodiment of the current detector 15 and theprocessing means 16 in any of the FIGS. 2, 5 and 6. In the embodiment ofFIG. 10, reference numeral 152 denotes a current transducer fortransducing the current flowing through the power supply line 2. 153denotes a converter for performing a root mean square conversion of thecurrent detected by current transducer 152, and to generate a currentlevel detection signal CL. 163 denotes a filtering and averaging circuitcomprising an RC element for averaging and delaying the current leveldetection signal CL. 164 denotes a circuit for transforming theprogrammable current threshold into a reference voltage Vref, e.g. bymeans of using a digital potentiometer, as such well known in the art,which converts the digital current threshold value into a tap positionof the potentiometer. 165 denotes a comparator circuit which comparesthe output signal of the filtering and averaging circuit 163 with theprogrammed reference voltage Vref. 166 denotes a driver circuit, e.g. aMOSFET transistor or bipolar transistor which receives at its gate theoutput signal from the comparator circuit 165. As soon as the outputsignal of the circuit 163 exceeds the programmed reference voltage Vref,the comparator circuit 165 generates a gate signal such that thetransistor 166 turns conductive and causes a tripping current to flowthrough the means 13 which will then cause the switch 11 to break theelectrical circuit. In this embodiment, the elements 163, 164, 165implement the processing means 16 using hardware components.

FIG. 11 shows yet another embodiment of the current detector 15 and theprocessing means 16. Elements similar to the elements shown in FIG. 10are denoted with the same reference numerals. With respect to theseelements reference is made to the description of FIG. 10. In FIG. 11,1631 denotes a voltage frequency converter for converting the currentlevel detection signal CL into a corresponding frequency. 1632 denotes afrequency divider which divides the frequency provided by the currentfrequency converter 1631 by a factor determined by the programmedcurrent threshold stored in the memory MEM of the electric circuitbreaker 1. The frequency divider outputs a divided signal ck forclocking a counter 1651. 1642 denotes a circuit for converting theprogrammed time interval associated with the programmed currentthreshold from the stored digital representation in the memory MEM intoa signal for controlling the frequency of an oscillator 1641. Theoscillator 1641 outputs a reset signal to the counter 1651 with afrequency in accordance with the programmed time interval Tj. If theoutput signal of the frequency divider CK occurs with a frequency higherby a given factor than the frequency of the reset signal, the counter1651 will output an overflow signal to the driver transistor 166 inorder to generate the tripping signal.

Accordingly, the embodiment shown in FIG. 11 implements the processingmeans 16 in hardware such that the processing means 16 can generate thetripping signal 14 depending on a stored programmable current thresholdcommand indicating a current threshold Ij and an associated responsetime interval Tj, and depending on the detecting current level flowingin the electrical circuit 3.

The embodiments so far described comprise a switch 11 which can betripped by the first means 13 and also by the second means 12advantageously provided as a back up. The switch 11 can be a mechanicalswitch with movable contacts 111 to break or close the electric circuit.Alternatively, the switch 11 can be composed of a series connection of amechanical switch and a solid state switch, e.g. a triac. The mechanicalswitch is mechanically coupled with the second means 12, and the solidstate switch receives a control signal from the first means 13 inaccordance with the tripping signal 14 from the processing means 16.

In the embodiments described above, the breaker characteristics areachieved by detecting the current flowing through the electric breaker,and controlling the breaker switch in accordance with one or moreprogrammable current thresholds and related response time intervals.Thermo-magnetic characteristics of the breaker can be provided as asafety margin, while the actual operating thresholds can be programmedinto the electric breaker. This allows to make the trigger thresholddependent e.g. on the present load in the electricity distributionnetwork, on the time of day, or on more complex parameters like type ofcustomer (e.g. hospital versus private consumer) and the present loadsituation in the electricity distribution network. The programmableelectric breaker thus allows a remote adaptation to changes in thesupply contract and/or effective counter measures in emergencysituations, e.g. when approaching the maximum load which the network canbear.

While the embodiments described above are based on a detection of thecurrent flowing in the electrical circuit 3, the skilled person willunderstand that it would be possible to achieve essentially the sameeffects if instead of or in addition to the detection of the currentflowing in the circuit 3, the active and/or reactive power fed into theelectrical circuit 3 is detected. Similarly, the programmable currentthresholds described above may define current thresholds or powerthresholds or a suitable complex entity composed of current and power.Whenever the foregoing description refers to the detection of currentlevels or the programming of current thresholds, the term current is tobe understood in this more general sense. Reference signs in the claimsshall not be construed to limit their scope.

1. An electric circuit breaker (1) for protecting an electrical circuit(3) against excessive current loads, comprising a switch (11) to bearranged in said electrical circuit (3); first means (13) for causingsaid switch (1 1) to break said electrical circuit (3) in response to atripping signal (14); means (17) for receiving (IF) and storing (MEM) aprogrammable current threshold command (CC); means (15) for detecting acurrent level (CL) in said electrical circuit (3); and processing means(16) for generating said tripping signal (14) depending on said storedprogrammable current threshold command (CC) and said detected currentlevel (CL); characterized by second means (12) for causing said switch(11) to break said electrical circuit (3) if a current flowing in saidelectrical circuit exceeds a predetermined rated current (I_(R) ) formore than a specified duration (31, 32).
 2. The electric circuit breaker(1) according to claim 1, said second means (12) comprising a thermalcurrent level detection element; and means for causing said switch (11)to break said electrical circuit (3) if said thermal current leveldetection element exceeds a temperature threshold.
 3. The electriccircuit breaker according to claim 1, said second means (12) comprisingelectromagnetic current level detection means including a coil; andmeans for causing said switch (11) to break said electrical circuit (3)if a magnetic force generated by said coil exceeds a threshold.
 4. Theelectric circuit breaker (1) according to claim 1, said second means(12) comprising a thermal current level detection means for thermallydetecting an amount of current (I) flowing in said electrical circuit;means for causing said switch to break said electrical circuit (3) ifsaid thermal current level detection means exceeds a temperaturethreshold determining the rated current (11) of said electrical circuitbreaker (1); electromagnetic current level detection means including acoil for generating a magnetic force in accordance with the amount ofcurrent (I) flowing in said electrical circuit (3); and means forcausing said switch means to break said electrical circuit if saidmagnetic force generated by said coil exceeds a force threshold (I₂),said electromagnetic current detection means and said thermal currentlevel detection means being dimensioned such that an electrical currentlevel (I₂) corresponding to said force threshold is higher than saidrated electrical current level (I₁).
 5. The electric circuit breaker (1)according to claim 1, wherein said switch (11) comprises a mechanicalinterruption element in series with a solid state interruption element;said second means (12) for causing said switch to break said electricalcircuit if a current (I) flowing in said electrical circuit (3) exceedsa predetermined rated current (I₁) is arranged to trip said mechanicalinterruption element; and said first means (13) for causing said switchto break said electrical circuit in response to a tripping signal (14)is arranged to trip said solid state interruption element.
 6. Thecircuit breaker according to claim 1, wherein said first means (13),said second means (12) and said switch (11) are integrated into a singleunit.
 7. The electric circuit breaker (1) according to claim 1, whereinsaid means (15) for detecting a current level in said electrical circuitcomprises means (R) for converting an electrical current flowing in saidelectrical circuit into a voltage; and means (151) for detecting saidvoltage and outputting a corresponding current level detection signal(CL).
 8. The electric circuit breaker (1) according to claim 7, whereinsaid means (15) for converting an electrical current into a voltagecomprises a shunt impedance (R) or an arrangement of coils magneticallycoupled to constitute a transformer or a hall effect device or amagnetoresistor or a Rogosky coil.
 9. The electric circuit breaker (1)according to claim 1, wherein said processing means (16) is adapted togenerate said tripping signal (14) after said detected current level(CL) has continuously exceeded said programmed current threshold (I₃,I₄, I₅) for a specified duration Tj.
 10. The electric circuit breaker(1) according to claim 9, wherein said specified duration can beprogrammed to depend on the detected level of current (CL) in saidelectric circuit (3).
 11. The electric circuit breaker according toclaim 9, comprising means (17) for receiving and storing a command whichspecifies said duration Tj.
 12. The electric circuit breaker (1)according to claim 10, comprising means for storing a second currentthreshold (I₁) higher than said programmed current threshold (I₃, I₄,I₅); said specified duration being a first duration, predetermined orprogrammed, if said detected current level (CL) is above said programmedcurrent threshold (I₃, I₄, I₅) and below said second current threshold(11), and a second duration, predetermined or programmed, and shorterthan said first duration if said detected current level (CL) is abovesaid second current threshold (I₁.)
 13. The electric circuit breaker (I)according to claim 12, comprising means to receive a second currentthreshold command; said second current threshold storing means beingadapted to store said second current threshold in accordance with saidreceived second current threshold command.
 14. The electric circuitbreaker (1) according to claim 12, wherein said programmable currentthreshold (I₃, I₄, I₅) is lower than said rated current level (I₁); andsaid second current threshold (I₁) is lower than the current level (I₂)corresponding to said force threshold.
 15. The electric circuit breaker(1) according to claim 9, wherein said processing means (16) is adaptedto provide a plurality of functional relations (331, 332, 333) eachspecifying for a plurality of current levels (I) a respective associatedduration (t); and select one of said functional relations (331, 332,333) in accordance with said current threshold command (CC).
 16. Theelectric circuit breaker (I) according to claim 15, wherein saidfunctional relations are stored in said processing means (16) in theform of tables or in the form of software routines for calculating saidfunctional relations.
 17. The electric circuit breaker (1) according toclaim 1, comprising means (17) for receiving a circuit close command;and means (13) for operating said switch (11) to close the electricalcircuit in response to said circuit close command.
 18. The electriccircuit breaker (1) according to claim 1, comprising means (17) forreceiving a circuit interrupt command; and means (13) for operating saidswitch (11) to break said electrical circuit (3) in response to saidcircuit interrupt command.
 19. The electric circuit breaker (1)according to claim 1, comprising powerline communication means (171, IF)for receiving said commands via a public electric power line (LV, 2)which feeds said electric circuit (3) through said switch (11).
 20. Thecircuit breaker according to claim 1, wherein said first means (13)comprises a coil (131) for electro magnetically driving a movable member(132) and an auxiliary switch (133) connected in series with said coil(131); said switch (11) and said auxiliary switch (133) beingmechanically coupled with said movable member (132) for actuationthereby; a displacement (θ133) required for opening said auxiliaryswitch (133) being larger than a displacement (θ11) required for openingsaid switch (11).
 21. An electricity meter (100) for measuring theamount of energy supplied to an electricity consumer (Hn) through anelectric circuit (3), comprising an electric circuit breaker (1)according to claim
 1. 22. The electricity meter (100) according to claim21, comprising means (18) for multiplying said detected current level(CL) with a supply voltage (U) of said electrical circuit (3) in orderto obtain a measure for the instantaneous active and reactive powerlevels supplied to said electric circuit (3); and means (18) forintegrating said obtained instantaneous power levels over time in orderto obtain the active and reactive energy supplied to said electricalcircuit (3).
 23. An electricity distribution network, comprising atleast one electrical power plant for generating electrical power to bedistributed to a plurality of consumers (H1, H2, . . . , Hn); anelectrical power distribution network (HV, MV, LV) for distributing thepower generated by said at least one power plant to said consumers (H1,H2, . . . , Hn); and a plurality of electric circuit breakers (1)according to any one of the claims 1 to 18 and/or a plurality ofelectricity meters (100) according to claim
 21. 24. The electricitydistribution network according to claim 23, comprising administrationand control facilities (21) for monitoring load conditions in said powerdistribution network (HV, MV, LV), and for generating at least one ofsaid commands for said electric circuit breakers (I) in accordance withsaid monitored load conditions.
 25. The electricity distribution networkaccording to claim 24, comprising a plurality of primary substations(Tp) arranged between high voltage portions (HV) and medium voltageportions (MV) of said electricity distribution network; a plurality ofsecondary substations (Ts) arranged between medium voltage portions (MV)and low voltage portions (LV) of said electricity distribution network;communication means (CBT) arranged at at least one of said secondarysubstations for receiving commands from said administration and controlfacilities (21), and for generating said current threshold commands (CC)and/or circuit close commands and/or circuit interrupt commands inaccordance with commands received from said administration and controlfacilities (21); power line communication means (24) for injecting saidcommands generated by said communication means (CBT) into a low voltageportion (LV, 2) of said electricity distribution network fortransmission to at least one of said electricity consumers (H1, . . . ,Hn); said administration and control facilities (21) and saidcommunication means (CBT) being arranged to communicate with each othervia a public telephone network (20).
 26. The electricity distributionnetwork according to claim 25, wherein said public telephone network isa wireless mobile telephone network (20, 23).